1. Field of the Invention
This invention relates to a n.times.n light matrix switch capable of switching the optical paths of n light signals supplied from n input terminals to output them to n output terminals, particularly relates to a light matrix switch for light-switching wavelength multiplexed light signals.
2. Description of Related Art
Conventionally, a n.times.n light matrix switch is structured by combining 2.times.2 light switch elements depending on the number of input terminals. The light signal is supplied from input terminals, the path is determined while the light signal is passing through the switch elements, and the light path is connected to any one of output terminals, then the light is outputted from the output terminal. Usually LiNbO.sub.3 waveguide type light switches have been used as the 2.times.2 light switch element. 2.times.2 light switch elements are arranged on a LiNbO.sub.3 substrate, and the light waveguide is used for connecting between switch elements.
When the light path of a light signal passing through a light matrix switch is switched, the path of other light signals the path of which are not switched is cut off and the cut-off causes blocking phenomenon. To avoid the blocking phenomenon, at least nC2 units of 2.times.2 light switches are required to construct a n.times.n light matrix switch having the structure comprising the combination of 2.times.2 light switches. It is easily understandable by considering the preposition that, in the operation for switching the path of a single light signal while full n input light signals are inputted, it is required to perform the operation for switching between the light signal which is already outputted to the output terminal to be switched and the light signal which is desired to be switched using any one of 2.times.2 light switch elements, that is, this operation is replaced with the operation that two inputs are selected out of n inputs for switching.
For example, at least 28 switch elements are necessary to construct a 8.times.8 matrix switch, and at least 120 2.times.2 light switch elements are necessary to construct a 16.times.16 matrix switch, this size is the significantly large scale structure. From the view point of the large number of light switch elements, the conventional structure is not suitable for a large scale matrix switch.
Though blocking phenomenon does not occur, a n.times.n light matrix switch having the structure of combined 2.times.2 switch elements as described herein above requires an increased number of 2.times.2 light switch elements with increasing of the number of input terminals. The whole structure is large, and the control means becomes complex because the number of objects to be controlled is the same as the number of elements.
The conventional n.times.n light matrix switch having another structure has been known which comprises a wavelength conversion circuit, optical coupler, and wavelength demultiplexer in addition to light signal input terminal and light signal output terminal. The light signal inputted to the input terminal is converted to a light wavelength corresponding to a specific output terminal by the wavelength conversion circuit, subjected to wavelength division multiplexing in the optical coupler, and then outputted to the wavelength demultiplexer. The wavelength-division-multiplexed light signal is wavelength-multiplexed to light signals with wavelengths .lambda.1 to .lambda.n by the wavelength demultiplexer and outputted to respective light output terminals. By combining these wavelength conversion, wavelength division multiplexing, and wavelength demultiplexing operations, the function of a n.times.n light matrix switch which connects between specific n input terminals and n output terminals is realized.
This structure is advantageous in comparison with the above-mentioned structure in that the structure can be small sized, however, the wavelength is shifted for switching the path of a light signal. In the switching transition condition, the wavelength of the sifted light signal can be the same wavelength of other signal which is not switched. The shifting can cause blocking phenomenon.
In the former conventional structural example, the input light is set in 1:1 by the path in the space, on the other hand, in the latter conventional structural example, the input light signal is converted to one specific wavelength corresponding to the output terminal, therefore in both cases, the input signal appears only at any one of output terminals. In other words, one input signal can not be outputted to a plurality of output terminals selectively, this is another disadvantage of the conventional light matrix switch.